#include <bits/stdc++.h>
using namespace std;
#define yes cout << "YES" << endl
#define no cout << "NO" << endl
using ll = long long;
ll l1, n, m;
ll a[50010];
bool check(ll x)
{
    ll cnt = 0;
    ll lst = 0;
    for (ll i = 1; i <= n; i++)
    {
        if (a[i] - lst < x)
        {
            cnt++;
        }
        else
            lst = a[i];
    }
    return cnt <= m;
}
void solve()
{
    cin >> l1 >> n >> m;
    for (ll i = 1; i <= n; i++)
    {
        cin >> a[i];
    }
    n++;
    a[n] = l1;
    ll l = 1, r = 1e9;
    while (l < r)
    {
        ll mid = (l + r+1) / 2;
        if (check(mid))
        {
            l = mid;
        }
        else
        {
            r = mid - 1;
        }
    }
    cout << l;
}
int main()
{
    int t = 1;
    // cin >> t;
    while (t--)
    {
        solve();
    }
    return 0;
}
